This invention relates generally to a method for manufacturing a fully sealed piston ring structure adapted for use in high pressure engines and pumps; more particularly, it relates to a method of joining piston ring components using silver solder which melts at a temperature which is low enough to avoid ring distortion.
The design of conventional piston rings which are used in internal combustion engines for automobiles, trucks, buses, and for industrial purposes, is a significant contributor to the pollution of the air resulting from the emissions of these engines, whether such reciprocating piston internal combustion engines are fueled by gasoline or diesel fuel. A conventional piston ring is understood to mean a single ring for a piston ring groove having some form of butt joint. Such piston rings which have a straight or butt joint where the two ends of the split ring come together are characterized by the problem of "blowby" or leakage of gases past the ring. What is referred to as "blowby" past the piston rings causes an increase in the exhaust emissions for the following reasons: blowby results in the reduction of compression above the piston and therefore less efficient engine operation; and, less efficient engine operation means that more fuel is required for a given power output, therefore more exhaust emissions. Also, conventional piston ring design requires greater clearance between the piston rings and piston groove walls, which inherently increases leakage around the piston rings. Furthermore, blowby results in contamination of the air/fuel mixture with oil and vapors from the crankcase, thereby increasing undesirable exhaust emissions.
While many designs of fully sealed rings have been proposed to solve the problems mentioned above, one difficulty is that the cost of manufacture of such rings has seemed to be economically unreasonable in relation to the cost of manufacture of conventional piston rings. The prior art teaches piston ring configurations consisting of two split ring members which are welded together to form a two-turn helical ring of the type described herein, and it also teaches integrally formed two-turn helical rings; but the prior art does not disclose how such rings may be manufactured or fabricated as a practical matter. The applicant is not aware of any practical method for welding together two ring members which are fabricated of piston ring alloy, which does not distort or deface the ring members or the ring combination severely. Typically, significant further finishing is required to true up the various faces of a welded ring. Too, in the case of spot welding, the structure of the ring metal would be weakened to such an extent as to contribute to premature breakage in use.
Another situation in which engines may experience unreasonable blowby past the piston rings arises from deformation of the cylinder walls, which may result from unequal expansion caused by non-uniform thickness of the cylinder wall casting or non-uniform heating of the cylinder wall. However, the resultant blowby from such a situation could be reduced if there could be a piston ring which is more flexible than conventional rings, and which is better able to follow such deformations of the cylinder wall.
One problem with conventional rings which have a butt joint is that hot gases flow through the joint--into and out of the groove space behind the ring, resulting in carbon buildup at the joint. This carbon buildup could be so severe that it might freeze the ring joint, unless some means is provided for breaking up the deposited carbon. A solution has usually been to provide sufficient clearance (or slop) between the ring and groove walls so as to allow axial movement of the ring joints relative to the groove; this clearance may be in range of 0.0025 to 0.0030 inches for the top groove of the piston, and about 0.0020 inches for the second and third compression ring grooves. As might be expected, providing this clearance inherently increases the blowby problem. It should be understood, therefore, that there has been a long-standing need for improved piston rings which can minimize or eliminate the problem of blowby.
A principal object of this invention is to provide a method for manufacturing a fully sealed piston ring which substantially prevents blowby past the piston ring while still being economical to manufacture.
Another object of this invention is to provide a method for manufacturing a fully sealed piston ring which is suitable for use with engines having ported cylinders as well as with engines having non-ported cylinders.
A further object of this invention is to provide a method for manufacturing a fully sealed piston ring which, in addition to substantially preventing blowby between the ring's ends (or between the ring and the piston groove), is more flexible so as to better follow cylinder irregularities or deformations--to thereby minimize blowby resulting from such irregularities or deformations.
Still another object of this invention is to provide a method for manufacturing a fully sealed piston ring, enabling the design of less clearances between the piston ring and the piston groove, and providing for less wear and longer life of these co-acting surfaces.
A still further object of this invention is to provide a method for manufacturing a fully sealed piston ring, including the joining of two split-ring members by a metal joining operation which neither damages, distorts nor defaces the ring members.
Still another object of this invention is to provide a method for economically manufacturing a fully sealed piston ring, i.e., a ring which substantially eliminates both axial blowby across the ring and radial blowby across the ring from the outer piston wall to the base of the piston ring groove.
These objects are accomplished in a method for fabricating a unitary, fully sealed piston ring including the following steps. First and second split ring members are formed with parallel and confronting planar side faces, and with concentric outer and inner faces, with at least the outer edge face being cylindrical. In each ring member there are formed circumferentially overlapping, radially contiguous fingers at the adjoining ends of the ring. These fingers include a radially outer finger consisting of a circumferential extension of the outer peripheral portion of the ring member, and a radially inner finger consisting of a circumferential extension of the radially inner portion of the ring member. Typical fingers are about one-fourth inch in length. Radially contiguous and confronting faces which are cylindrical in nature are formed on these figures, with the faces being generated about the same axis as the outer cylinder face. The cylindrical finger faces and the side faces of the ring members are finished for sealing relation with respective co-acting surfaces. The first and second ring members are assembled in overlying, side-by-side, contiguous relation, with the first ends of the ring members circumferentially overlapping each other by a distance that preferably is at least one-half inch. With this arrangement, the joint which is made up between the first and second ends of a given ring member will overlie a solid (uninterrupted) portion of the other ring member. The two ring members are permanently joined into a unitary assembly by means of at least one silver solder joint between the overlapping and contiguous first ends of the members, with the joint preferably being located adjacent each of the outer fingers, so as to secure each of the outer fingers rigidly to the adjacent ring member. If the ring members are suitably finished before the joining step, and a suitable silver solder joining material is used, there should be no need for any subsequent finishing steps before the outer cylindrical surfaces of the assembled ring members are ready for a sealing relation with a co-acting cylinder wall.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawing.